They close at 4pm, in general, because that's when it starts to get dark in December, when the season begins. And it's too crazy to be changing ?closing time? during the season to match later and later sunset times. Also, the resorts likely pay employees for a standard 8 hour workday.

The standard 4:00 PM (or 16:00) closing time for ski lifts is a critical balance of safety, visibility, and mountain logistics. As the sun begins to set in winter, shadows lengthen and the "flat light" makes it difficult for skiers to see terrain changes, icy patches, or obstacles, significantly increasing the risk of injury. Furthermore, the temperature drops rapidly, causing the snow surface to freeze into dangerous ice. This early closure allows the Ski Patrol to perform a "sweep" of the entire mountain to ensure no injured or lost skiers are left behind before dark. It also provides the essential window for snow grooming teams and snowmakers to safely operate heavy machinery and prepare the runs for the next morning. By 4:00 PM, physical fatigue also sets in for most guests, and closing the lifts encourages them to head indoors, reducing the likelihood of accidents caused by exhaustion.